A light emitting device including a light emitting element such as light emitting diode (LED) is used in various types of light sources. According to the development of semiconductor techniques, development of high-power light emitting elements is accelerating. To stably correspond to large amounts of light and heat emitted from such a light emitting element, radiating performance of the light emitting element is required.
In addition, according to the tendency of highly-integrated and high-power electronic parts, there is a growing attention for radiation of a printed circuit board on which electronic parts are mounted.
Generally, for an insulating layer of a light emitting element or printed circuit board, an epoxy resin composition including an epoxy compound, a curing agent and an inorganic filler may be used.
Here, the inorganic filler may include a ceramic-based inorganic filler such as boron nitride, silicon carbide, aluminum oxide, or aluminum nitride, or a carbon-based inorganic filler such as a carbon nanotube, graphite, or graphene. According to the type and content of the inorganic filler included in the epoxy resin composition, dispersity, insulability and thermal conductivity of the epoxy resin composition may be changed.
One of the inorganic fillers, boron nitride, while having a very high thermal conductivity, has a low wettability with the epoxy compound, a low dispersity, a low adhesive strength to a substrate, and a low processability.
In addition, planar boron nitride has an excellent thermal conductivity, but has an anisotropic thermal conductivity. To solve such a problem, an agglomerate of the planar boron nitrides may be used, but the thermal conductivity may be reduced due to a void in the agglomerate, and the agglomerate is easily breakable due to a weak binding strength between the planar boron nitrides.